The strawberry notch gene functions with Notch in common developmental pathways

An isoform quantitative trait locus in SBNO2 links genetic susceptibility to Crohn's disease with defective antimicrobial activity

Despite major advances in linking single genetic variants to single causal genes, the significance of genetic variation on transcript-level regulation of expression, transcript-specific functions, and relevance to human disease has been poorly investigated. Strawberry notch homolog 2 (SBNO2) is a candidate gene in a susceptibility locus with different variants associated with Crohn's disease and bone mineral density. The SBNO2 locus is also differentially methylated in Crohn's disease but the functional mechanisms are unknown. Here we show that the isoforms of SBNO2 are differentially regulated by lipopolysaccharide and IL-10. We identify Crohn's disease associated isoform quantitative trait loci that negatively regulate the expression of the noncanonical isoform 2 corresponding with the methylation signals at the isoform 2 promoter in IBD and CD. The two isoforms of SBNO2 drive differential gene networks with isoform 2 dominantly impacting antimicrobial activity in macrophages. Our data highlight the role of isoform quantitative trait loci to understand disease susceptibility and resolve underlying mechanisms of disease.

Autophagy as a new player in the regulation of clock neurons physiology of Drosophila melanogaster

Axonal terminals of the small ventral lateral neurons (sLNvs), the circadian clock neurons of Drosophila, show daily changes in their arborization complexity, with many branches in the morning and their shrinkage during the night. This complex phenomenon is precisely regulated by several mechanisms. In the present study we describe that one of them is autophagy, a self-degradative process, also involved in changes of cell membrane size and shape. Our results showed that autophagosome formation and processing in PDF-expressing neurons (both sLNv and lLNv) are rhythmic and they have different patterns in the cell bodies and terminals. These rhythmic changes in the autophagy activity seem to be important for neuronal plasticity. We found that autophagosome cargos are different during the day and night, and more proteins involved in membrane remodeling are present in autophagosomes in the morning. In addition, we described for the first time that Atg8-positive vesicles are also present outside the sLNv terminals, which suggests that secretory autophagy might be involved in regulating the clock signaling network. Our data indicate that rhythmic autophagy in clock neurons affect the pacemaker function, through remodeling of terminal membrane and secretion of specific proteins from sLNvs.

SBNO2 is a critical mediator of STAT3-driven hematological malignancies

Gain-of-function mutations in the signal transducer and activator of transcription 3 (STAT3) gene are recurrently identified in patients with large granular lymphocytic leukemia (LGLL) and in some cases of natural killer (NK)/T-cell and adult T-cell leukemia/lymphoma. To understand the consequences and molecular mechanisms contributing to disease development and oncogenic transformation, we developed murine hematopoietic stem and progenitor cell models that express mutated STAT3Y640F. These cells show accelerated proliferation and enhanced self-renewal potential. We integrated gene expression analyses and chromatin occupancy profiling of STAT3Y640F-transformed cells with data from patients with T-LGLL. This approach uncovered a conserved set of direct transcriptional targets of STAT3Y640F. Among these, strawberry notch homolog 2 (SBNO2) represents an essential transcriptional target, which was identified by a comparative genome-wide CRISPR/Cas9-based loss-of-function screen. The STAT3-SBNO2 axis is also present in NK-cell leukemia, T-cell non-Hodgkin lymphoma, and NPM-ALK-rearranged T-cell anaplastic large cell lymphoma (T-ALCL), which are driven by STAT3-hyperactivation/mutation. In patients with NPM-ALK+ T-ALCL, high SBNO2 expression correlates with shorter relapse-free and overall survival. Our findings identify SBNO2 as a potential therapeutic intervention site for STAT3-driven hematopoietic malignancies.

Strawberry notch homolog 2 regulates the response to interleukin-6 in the central nervous system

BACKGROUND

The cytokine interleukin-6 (IL-6) modulates a variety of inflammatory processes and, context depending, can mediate either pro- or anti-inflammatory effects. Excessive IL-6 signalling in the brain is associated with chronic inflammation resulting in neurodegeneration. Strawberry notch homolog 2 (Sbno2) is an IL-6-regulated gene whose function is largely unknown. Here we aimed to address this issue by investigating the impact of Sbno2 disruption in mice with IL-6-mediated neuroinflammation.

METHODS

Mice with germline disruption of Sbno2 (Sbno2-/-) were generated and crossed with transgenic mice with chronic astrocyte production of IL-6 (GFAP-IL6). Phenotypic, molecular and transcriptomic analyses were performed on tissues and primary cell cultures to clarify the role of SBNO2 in IL-6-mediated neuroinflammation.

RESULTS

We found Sbno2-/- mice to be viable and overtly normal. By contrast GFAP-IL6 × Sbno2-/- mice had more severe disease compared with GFAP-IL6 mice. This was evidenced by exacerbated neuroinflammation and neurodegeneration and enhanced IL-6-responsive gene expression. Cell culture experiments on primary astrocytes from Sbno2-/- mice further showed elevated and sustained transcript levels of a number of IL-6 stimulated genes. Notably, despite enhanced disease in vivo and gene expression both in vivo and in vitro, IL-6-stimulated gp130 pathway activation was reduced when Sbno2 is disrupted.

CONCLUSION

Based on these results, we propose a role for SBNO2 as a novel negative feedback regulator of IL-6 that restrains the excessive inflammatory actions of this cytokine in the brain.

Filtering of the Gene Signature as the Predictors of Cisplatin-Resistance in Ovarian Cancer

BACKGROUND

Gene expression profiling and prediction of drug responses based on the molecular signature indicate new molecular biomarkers which help to find the most effective drugs according to the tumor characteristics.

OBJECTIVES

In this study two independent datasets, GSE28646 and GSE15372 were subjected to meta-analysis based on Affymetrix microarrays.

MATERIAL AND METHODS

In-silico methods were used to determine differentially expressed genes (DEGs) in the previously reported sensitive and resistant A2780 cell lines to Cisplatin. Gene Fuzzy Scoring (GFS) and Principle Component Analysis (PCA) were then used to eliminate batch effects and reduce data dimension, respectively. Moreover, SVM method was performed to classify sensitive and resistant data samples. Furthermore, Wilcoxon Rank sum test was performed to determine DEGs. Following the selection of drug resistance markers, several networks including transcription factor-target regulatory network and miRNA-target network were constructed and Differential correlation analysis was performed on these networks.

RESULTS

The trained SVM successfully classified sensitive and resistant data samples. Moreover, Performing DiffCorr analysis on the sensitive and resistant samples resulted in detection of 27 and 25 significant (with correlation ≥|0.9|) pairs of genes that respectively correspond to newly constructed correlations and loss of correlations in the resistant samples.

CONCLUSIONS

Our results indicated the functional genes and networks in Cisplatin resistance of ovarian cancer cells and support the importance of differential expression studies in ovarian cancer chemotherapeutic agent responsiveness.

microRNAs in Macrobrachium olfersii embryos: Identification, their biogenesis components and potential targets

In embryonic development, microRNAs (miRNAs) regulate the complex gene expression associated with the complexity of embryogenesis. Today, few studies have been conducted on the identification of miRNAs and components of miRNA biogenesis on embryonic development in crustaceans, especially in prawns. In this context, the aim of this study was to identify in silico components of miRNA biogenesis, and miRNAs and potential target genes during embryonic development in the prawn Macrobrachium olfersii through small RNAs and transcriptome analyses. Using the miRDeep2 program, we identified 17 miRNA precursors in M. olfersii, which seven (miR-9, miR-10, miR-92, miR-125, miR-305, miR-1175, and miR-2788) were reported in the miRBase database, indicating high evolutionary conservation of these sequences among animals. The other 10 miRNAs of M. olfersii were novel miRNAs and only similar to Macrobrachium niponnense miRNAs, indicating genus-specific miRNAs. In addition, eight key components of miRNA biogenesis (DROSHA, PASHA/DGCR8, XPO5, RAN, DICER, TRBP2, AGO, and PIWI) were identified in M. olfersii embryos unigenes. In the annotation of miRNA targets, 516 genes were similar to known sequences in the GenBank database. Regarding the conserved miRNAs, we verified that they were differentially expressed during embryonic development in M. olfersii. In conclusion, this is the first study that identifies conserved and novel miRNAs in the prawn M. olfersii with some miRNA target genes involved in embryonic development. Our results will allow further studies on the function of these miRNAs and miRNA biogenesis components during embryonic development in M. olfersii and other prawns of commercial interest.

Parent-of-Origin-Dependent Gene Expression in Male and Female Schistosome Parasites

Schistosomes are the causative agents of schistosomiasis, a neglected tropical disease affecting over 230 million people worldwide. Additionally to their major impact on human health, they are also models of choice in evolutionary biology. These parasitic flatworms are unique among the common hermaphroditic trematodes as they have separate sexes. This so-called “evolutionary scandal” displays a female heterogametic genetic sex-determination system (ZZ males and ZW females), as well as a pronounced adult sexual dimorphism. These phenotypic differences are determined by a shared set of genes in both sexes, potentially leading to intralocus sexual conflicts. To resolve these conflicts in sexually selected traits, molecular mechanisms such as sex-biased gene expression could occur, but parent-of-origin gene expression also provides an alternative. In this work we investigated the latter mechanism, that is, genes expressed preferentially from either the maternal or the paternal allele, in Schistosoma mansoni species. To this end, transcriptomes from male and female hybrid adults obtained by strain crosses were sequenced. Strain-specific single nucleotide polymorphism (SNP) markers allowed us to discriminate the parental origin, while reciprocal crosses helped to differentiate parental expression from strain-specific expression. We identified genes containing SNPs expressed in a parent-of-origin manner consistent with paternal and maternal imprints. Although the majority of the SNPs was identified in mitochondrial and Z-specific loci, the remaining SNPs found in male and female transcriptomes were situated in genes that have the potential to explain sexual differences in schistosome parasites. Furthermore, we identified and validated four new Z-specific scaffolds.

Comparative RNA-sequencing analysis of ER-based HSP90 functions and signal pathways in Tribolium castaneum

Tribolium castaneum, the red flour beetle, is a major agriculture pest that damages stored grains and cereal products. Heat-shock protein 90 of T. castaneum (Tchsp90) has been reported to play pivotal roles in heat stress response, development, reproduction, and life span. However, the signaling pathway of Tchsp90 remains unclear. Thus, the global transcriptome profiles between RNA interference (RNAi)-treated insects (ds-Tchsp90) and control insects of T. castaneum were investigated and compared by RNA sequencing. In all, we obtained 14,145,451 sequence reads, which assembled into 13,243 genes. Among these genes, 461 differentially expressed genes (DEGs) were identified between the ds-Tchsp90 and control samples. These DEGs were classified into 44 gene ontology (GO) functional groups, including the cellular process, the response to stimulus, the immune system process, the development process, and reproduction. Interestingly, knocking down the expression of Tchsp90 suppressed both the DNA replication and cell division signaling pathways, which most likely modulated the effects of Tchsp90 on development, reproduction, and life span. Moreover, the DEGs encoding AnnexinB9, frizzled-4, sno, Fem1B, TSL, and CSW might be related to the regulation of the development and reproduction of ds-Tchsp90 insects. The DEGs including TLR6, PGRP2, defensin1, and defensin2 were involved in heat stress and immune response simultaneously, which suggested that cross talk might exist between immunity and stress response. Additionally, RNAi of Tchsp90 altered large-scale serine protease (sp) gene expression patterns and amplified the SP signaling pathway to regulate the development and reproduction as well as the stress response and innate immunity in T. castaneum. All these results shed new light onto the regulatory mechanism of Tchsp90 involved in insect physiology and could further facilitate research into appropriate and sustainable pest control management.

Notch and Hippo signaling converge on Strawberry Notch 1 (Sbno1) to synergistically activate Cdx2 during specification of the trophectoderm

The first binary cell fate decision occurs at the morula stage and gives rise to two distinct types of cells that constitute the trophectoderm (TE) and inner cell mass (ICM). The cell fate determinant, Cdx2, is induced in TE cells and plays an essential role in their differentiation and maintenance. Notch and Hippo signaling cascades are assumed to converge onto regulatory elements of Cdx2, however, the underlying molecular mechanisms are largely unknown. Here, we show involvement of Strawberry Notch1 (Sbno1), a novel chromatin factor of the helicase superfamily 2, during preimplantation development. Sbno1 knockout embryos die at the preimplantation stage without forming a blastocoel, and Cdx2 is not turned on even though both Yap and Tead4 reside normally in nuclei. Accordingly, Sbno1 acts on the trophectoderm-enhancer (TEE) of Cdx2, ensuring its robust and synergistic activation by the Yap/Tead4 and NICD/Rbpj complexes. Interestingly, this synergism is enhanced when cells are mechanically stretched, which might reflect that TE cells are continuously stretched by the expanding ICM and blastocoel cavity. In addition, the histone chaperone, FACT (FAcilitates Chromatin Transcription) physically interacts with Sbno1. Our data provide new evidence on TE specification, highlighting unexpected but essential functions of the highly conserved chromatin factor, Sbno1.

Neurodegeneration in a Drosophila model of adrenoleukodystrophy: the roles of the Bubblegum and Double bubble acyl-CoA synthetases

Debilitating neurodegenerative conditions with metabolic origins affect millions of individuals worldwide. Still, for most of these neurometabolic disorders there are neither cures nor disease-modifying therapies, and novel animal models are needed for elucidation of disease pathology and identification of potential therapeutic agents. To date, metabolic neurodegenerative disease has been modeled in animals with only limited success, in part because existing models constitute analyses of single mutants and have thus overlooked potential redundancy within metabolic gene pathways associated with disease. Here, we present the first analysis of a very-long-chain acyl-CoA synthetase (ACS) double mutant. We show that the Drosophila bubblegum(bgm) and double bubble(dbb) genes have overlapping functions, and that the consequences of double knockout of both bubblegum and double bubble in the fly brain are profound, affecting behavior and brain morphology, and providing the best paradigm to date for an animal model of adrenoleukodystrophy (ALD), a fatal childhood neurodegenerative disease associated with the accumulation of very-long-chain fatty acids. Using this more fully penetrant model of disease to interrogate brain morphology at the level of electron microscopy, we show that dysregulation of fatty acid metabolism via disruption of ACS function in vivois causal of neurodegenerative pathologies that are evident in both neuronal cells and their supporting cell populations, and leads ultimately to lytic cell death in affected areas of the brain. Finally, in an extension of our model system to the study of human disease, we describe our identification of an individual with leukodystrophy who harbors a rare mutation in SLC27a6(encoding a very-long-chain ACS), a human homolog of bgm and dbb.

Strawberry notch homolog 2 is a novel inflammatory response factor predominantly but not exclusively expressed by astrocytes in the central nervous system

Interleukin‐6 (IL‐6) participates in the host response to injury and infection in the central nervous system (CNS). We identified strawberry notch homolog 2 (Sbno2) as an IL‐6‐stimulated gene in murine astrocytes. Sbno2 is a mouse homolog of the sno gene in Drosophila but little is known about the regulation or function of the mammalian gene. Here we examined the regulation of the Sbno2 gene in astrocytes in vitro and in the murine CNS following systemic endotoxin administration. In murine and human cultured astrocytes, Sbno2 gene expression was significantly upregulated in a dose‐ and time‐dependent fashion by hyper‐IL‐6 (IL‐6 + soluble IL‐6 receptor). The level of Sbno2 mRNA was also upregulated significantly in murine astrocytes by other glycoprotein130 cytokine‐family members and the pro‐inflammatory cytokines interleukin‐1 beta and tumor necrosis factor alpha. These changes were reflected by corresponding alterations in the level of the SBNO2 protein. Inhibiting protein synthesis resulted in higher Sbno2 mRNA and did not abolish the upregulation of Sbno2 mRNA mediated by hyper‐IL‐6. Inhibition of transcription led to a rapid reduction in hyper‐IL‐6‐induced Sbno2 mRNA in astrocytes suggesting that the Sbno2 mRNA is quite unstable. Following intra‐peritoneal lipopolysaccharide injection in mice, Sbno2 mRNA levels in the brain were significantly increased. Cellular localization studies revealed that this increase in Sbno2 mRNA occurred predominantly in astrocytes and in the choroid plexus and in some microglia, endothelial cells, and neurons. These findings are consistent with SBNO2 functioning as an acute inflammatory response gene in astrocytes as well as other cells in the CNS. GLIA 2015;63:1738–1752

Assessing the utility of intermediate phenotypes for genetic mapping of psychiatric disease

Intermediate phenotypes are traits positioned somewhere between genetic variation and disease. They represent a target for attempts to find disease-associated genetic variants and elucidation of mechanisms. Psychiatry has been particularly enamoured with intermediate phenotypes, due to uncertainty about disease aetiology, inconclusive results in early psychiatric genetic studies, and their appeal relative to traditional diagnostic categories. In this review, we argue that new genetic findings are relevant to the question of the utility of these constructs. In particular, results from genome-wide association studies of psychiatric disorders now allow an assessment of the potential role of particular intermediate phenotypes. Based on such an analysis, as well as other recent results, we conclude that intermediate phenotypes are likely to be most valuable in understanding mechanism.

Common variants at 12q15 and 12q24 are associated with infant head circumference

To identify genetic variants associated with head circumference in infancy, we performed a meta-analysis of seven genome-wide association studies (GWAS) (N = 10,768 individuals of European ancestry enrolled in pregnancy and/or birth cohorts) and followed up three lead signals in six replication studies (combined N = 19,089). rs7980687 on chromosome 12q24 (P = 8.1 × 10(-9)) and rs1042725 on chromosome 12q15 (P = 2.8 × 10(-10)) were robustly associated with head circumference in infancy. Although these loci have previously been associated with adult height, their effects on infant head circumference were largely independent of height (P = 3.8 × 10(-7) for rs7980687 and P = 1.3 × 10(-7) for rs1042725 after adjustment for infant height). A third signal, rs11655470 on chromosome 17q21, showed suggestive evidence of association with head circumference (P = 3.9 × 10(-6)). SNPs correlated to the 17q21 signal have shown genome-wide association with adult intracranial volume, Parkinson's disease and other neurodegenerative diseases, indicating that a common genetic variant in this region might link early brain growth with neurological disease in later life.

Expression of strawberry notch family genes during zebrafish embryogenesis

Our previous study suggested a possible role for Sbno1, a mouse homologue of strawberry notch gene during brain development. In this report, we cloned the zebrafish homologues of sbno, and examined their expression pattern during embryogenesis by whole-mount in situ hybridization. Zebrafish have three sbno genes: one Sbno1 homologue and two Sbno2 homologues, sbno2a and sbno2b. We observed that the expression of sbno1 and sbno2a was initially ubiquitous and gradually became predominant in the central nervous system as development progressed. The expression of sbno2b was observed in non-neural tissues in contrast to the other two genes. sbno1 and sbno2a exhibited higher expression in distinct regions within the nervous system of pharyngula-stage embryos, suggesting possible differing roles for sbno1 and sbno2a during later stages of embryogenesis. Together, the observed gene expression patterns suggest an important role of sbno-family genes during development of the vertebrate central nervous system.

Origin and evolution of the Notch signalling pathway: an overview from eukaryotic genomes

Background

Of the 20 or so signal transduction pathways that orchestrate cell-cell interactions in metazoans, seven are involved during development. One of these is the Notch signalling pathway which regulates cellular identity, proliferation, differentiation and apoptosis via the developmental processes of lateral inhibition and boundary induction. In light of this essential role played in metazoan development, we surveyed a wide range of eukaryotic genomes to determine the origin and evolution of the components and auxiliary factors that compose and modulate this pathway.

Results

We searched for 22 components of the Notch pathway in 35 different species that represent 8 major clades of eukaryotes, performed phylogenetic analyses and compared the domain compositions of the two fundamental molecules: the receptor Notch and its ligands Delta/Jagged. We confirm that a Notch pathway, with true receptors and ligands is specific to the Metazoa. This study also sheds light on the deep ancestry of a number of genes involved in this pathway, while other members are revealed to have a more recent origin. The origin of several components can be accounted for by the shuffling of pre-existing protein domains, or via lateral gene transfer. In addition, certain domains have appeared de novo more recently, and can be considered metazoan synapomorphies.

Conclusion

The Notch signalling pathway emerged in Metazoa via a diversity of molecular mechanisms, incorporating both novel and ancient protein domains during eukaryote evolution. Thus, a functional Notch signalling pathway was probably present in Urmetazoa.

Identification of Myc-associated protein with JmjC domain as a novel therapeutic target oncogene for lung cancer

Through genome-wide expression profile analysis for non-small cell lung cancers (NSCLC), we found overexpression of a Myc-associated protein with JmjC domain (MAPJD) gene in the great majority of NSCLC cases. Induction of exogenous expression of MAPJD into NIH3T3 cells conferred growth-promoting activity. Concordantly, in vitro suppression of MAPJD expression with small interfering RNA effectively suppressed growth of NSCLC cells, in which MAPJD was overexpressed. We found four candidate MAPJD target genes, SBNO1, TGFBRAP1, RIOK1, and RASGEF1A, which were the most significantly induced by exogenous MAPJD expression. Through interaction with MYC protein, MAPJD transactivates a set of genes, including kinases and cell signal transducers that are possibly related to proliferation of lung cancer cells. As our data imply that MAPJD is a novel member of the MYC transcriptional complex and its activation is a common feature of lung cancer, selective suppression of this pathway could be a promising therapeutic target for treatment of lung cancers.

A mouse homologue of Strawberry Notch is transcriptionally regulated by Reelin signal

Reelin is a glycoprotein secreted by specific neuronal populations of the adult and developing nervous system of vertebrates. The morphological abnormalities in the brain of reeler, the Reelin deficient mutant mice, indicate that Reelin is essential for the brain morphogenesis. However, biochemical function of Reelin signal is not well understood. Here, we examined possible function of Reelin signal in regulation of gene expression by performing a microarray analysis. We found that expression level of a mouse homologue of Strawberry Notch (mSno1) is markedly reduced in the reeler embryos. In situ hybridization showed that mSno1 is expressed in the developing nervous system colocalizing with expression of ApoER2, a Reelin receptor. Treatment of P19 cells with Reelin protein enhanced mSno1 expression. Overexpression of ApoER2 with Reelin treatment gave a synergistic effect on mSno1 expression level. These observations suggest that Reelin signal is involved in embryonic expression of a novel vertebrate gene, mSno1.

The novel plant homeodomain protein rhinoceros antagonizes Ras signaling in the Drosophila eye

The sequential specification of cell fates in the Drosophila eye requires repeated activation of the epidermal growth factor receptor (EGFR)/Ras/MAP kinase (MAPK) pathway. Equally important are the multiple layers of inhibitory regulation that prevent excessive or inappropriate signaling. Here we describe the molecular and genetic analysis of a previously uncharacterized gene, rhinoceros (rno), that we propose functions to restrict EGFR signaling in the eye. Loss of rno results in the overproduction of photoreceptors, cone cells, and pigment cells and a corresponding reduction in programmed cell death, all phenotypes characteristic of hyperactivated EGFR signaling. Genetic interactions between rno and multiple EGFR pathway components support this hypothesis. rno encodes a novel but evolutionarily conserved nuclear protein with a PHD zinc-finger domain, a motif commonly found in chromatin-remodeling factors. Future analyses of rno will help to elucidate the regulatory strategies that modulate EGFR signaling in the fly eye.

Developmental signaling: shrimp and strawberries help flies make cones

EGF receptor and Notch signaling are involved in a wide variety of developmental processes. A new study has revealed a serial linkage between them, via Ebi and Strawberry Notch, which is important in determining the cone cell fate in the Drosophila eye.

An EGFR/Ebi/Sno pathway promotes delta expression by inactivating Su(H)/SMRTER repression during inductive notch signaling

The Notch and Epidermal Growth Factor Receptor (EGFR) pathways both regulate proliferation and differentiation, and the cellular response to each is often influenced by the other. Here, we describe a mechanism that links them in a sequential fashion, in the developing compound eye of Drosophila. EGFR activation induces photoreceptor (R cell) differentiation and promotes their expression of Delta. This Notch ligand then induces neighboring cells to become nonneuronal cone cells. ebi and strawberry notch (sno) regulate EGFR-dependent Delta transcription by antagonizing a repressor function of Suppressor of Hairless (Su(H)). Sno binds to Su(H), and Ebi, an F-box/WD40 protein, forms a complex with Su(H) and the corepressor SMRTER. EGFR-activated transcriptional derepression requires ebi and sno, is proteasome-dependent, and correlates with the translocation of SMRTER to the cytoplasm.

Different mechanisms underlie phenotypic plasticity and interspecific variation for a reproductive character in drosophilids (Insecta: Diptera)

The insect ovary is a modular structure, the functional unit of which is the ovariole. Ovariole number is positively correlated with potential reproductive output. Among drosophilids (Insecta: Diptera), ovariole number shows both phenotypic plasticity and substantial interspecific and interpopulational variation. Here we examine the mechanistic connection between phenotypic plasticity and genetically fixed variation in ovariole number within the melanogaster species group. When a laboratory population of Drosophila melanogaster was reared under reduced food conditions, differences in ovariole number were entirely due to alterations in cell differentiation during the wandering stage at the very end of larval development. Cell growth and cell death were not affected. When these same flies were reared under a variety of temperatures, ovariole number differences arose during the latter half of the third (final) larval instar. Cell differentiation was affected, although cell number was not, and ovariole number differences were established before metamorphosis. In contrast, genetically fixed, interspecific and interpopulational variability in ovariole number was caused by alterations in the dynamics of cell differentiation and by cell number differences. Furthermore, the stages affected were different in different species and populations in the melanogaster species group, ranging from the first (D. sechellia) through the middle of the third (D. simulans and D. mauritiana) larval stage. Therefore, the mechanistic bases for plasticity-based variability are largely distinct from the mechanistic bases for interspecific and interpopulational variability. Our results suggest that phenotypic plasticity indicates evolutionary flexibility in underlying ontogenetic processes.

A genetic screen of the Drosophila X chromosome for mutations that modify Deformed function

We have screened the Drosophila X chromosome for genes whose dosage affects the function of the homeotic gene Deformed. One of these genes, extradenticle, encodes a homeodomain transcription factor that heterodimerizes with Deformed and other homeotic Hox proteins. Mutations in the nejire gene, which encodes a transcriptional adaptor protein belonging to the CBP/p300 family, also interact with Deformed. The other previously characterized gene identified as a Deformed interactor is Notch, which encodes a transmembrane receptor. These three genes underscore the importance of transcriptional regulation and cell-cell signaling in Hox function. Four novel genes were also identified in the screen. One of these, rancor, is required for appropriate embryonic expression of Deformed and another homeotic gene, labial. Both Notch and nejire affect the function of another Hox gene, Ultrabithorax, indicating they may be required for homeotic activity in general.

The LIN-12/Notch signaling pathway and its regulation

Notch, LIN-12, and GLP-1 are receptors that mediate a broad range of cell interactions during Drosophila and nematode development. Signaling by these receptors relies on a conserved pathway with three core components: DSL ligand, LNG receptor, and a CSL effector that links the receptor to its transcriptional response. Although key functional regions have been identified in each class of proteins, the mechanism for signal transduction is not yet understood. Diverse regulatory mechanisms influence signaling by the LIN-12/Notch pathway. Inductive signaling relies on the synthesis of ligand and receptor in distinct but neighboring cells. By contrast, lateral signaling leads to the transformation of equivalent cells that express both ligand and receptor into nonequivalent cells that express either ligand or receptor. This transformation appears to rely on regulatory feedback loops within the LIN-12/Notch pathway. In addition, the pathway can be regulated by intrinsic factors that are asymmetrically segregated during cell division or by extrinsic cues via other signaling pathways. Specificity in the pathway does not appear to reside in the particular ligand or receptor used for a given cell-cell interaction. The existence of multiple ligands and receptors may have evolved from the stringent demands placed upon the regulation of genes encoding them.

eyelid antagonizes wingless signaling during Drosophila development and has homology to the Bright family of DNA-binding proteins

In Drosophila, pattern formation at multiple stages of embryonic and imaginal development depends on the same intercellular signaling pathways. We have identified a novel gene, eyelid (eld), which is required for embryonic segmentation, development of the notum and wing margin, and photoreceptor differentiation. In these tissues, eld mutations have effects opposite to those caused by wingless (wg) mutations. eld encodes a widely expressed nuclear protein with a region homologous to a novel family of DNA-binding domains. Based on this homology and on the phenotypic analysis, we suggest that Eld could act as a transcription factor antagonistic to the Wg pathway.

strawberry notch encodes a conserved nuclear protein that functions downstream of Notch and regulates gene expression along the developing wing margin of Drosophila

The dorsal/ventral (D/V) boundary functions as an organizer in the growth and patterning of the Drosophila wing disc and gives rise to the wing margin in the adult fly. Here we show that strawberry notch (sno) is a downstream component of the Notch signaling pathway and is important for the specification of this organizer. sno encodes a novel nuclear protein conserved in C. elegans, mouse, and humans. Mutations in wing margin genes interact dominantly with sno and loss of sno function results in loss of expression of wingless, vestigial, cut, and E(spl)-m8 at the D/V boundary. In regulating these genes, sno functions in close cooperation with Suppressor of Hairless and Hairless. Finally, sno has no role in lateral inhibition suggesting that it may contribute to the specificity between lateral and inductive Notch signaling pathways.

Undifferentiated cells in the developing Drosophila eye influence facet assembly and require the Fat facets ubiquitin-specific protease

The Drosophila compound eye develops by a complex series of cell interactions where multiple positive and inhibitory cues guide cells in each facet into their positions and fates. The results of many genetic and molecular experiments have led to the view that facet assembly is directed by cells within developing ommatidial preclusters. Here fat facets mutants and the cloned fat facets gene were used to show that, in order to limit the number of photoreceptors in a facet to eight, undifferentiated cells surrounding assembling facets send an inhibitory signal to extraneous cells within the facet preclusters. Generation of the inhibitory signal requires the ubiquitin-specific protease encoded by the fat facets gene and is thus regulated by ubiquitin-dependent proteolysis.

Patterning of cells in the Drosophila eye by Lozenge, which shares homologous domains with AML1

The lozenge (lz) gene encodes a transcription factor involved in prepatterning photoreceptor precursors in the developing Drosophila eye. The central region of the predicted Lz protein product is homologous to AML1, a transcription factor associated with human leukemias, and to the Drosophila protein Runt. We show here that Lz plays a crucial role in governing the fate of two groups of cells that are born in a single round of mitosis in the larval eye disc. Lz helps define a subset of these cells as an equipotential group that is competent to respond to the Sevenless developmental signal. This is achieved by negative regulation of seven-up, a member of the steroid hormone receptor superfamily in these cells. In contrast, in a second group of cells, the Lz protein confers proper photoreceptor identity by positively regulating the homeo box gene Bar. Additionally, our genetic analysis suggests that Lz interacts with the Ras pathway to determine photoreceptor cell fate. This study suggests that the strategies involved in cell fate determination in the Drosophila eye are remarkably similar to those utilized during vertebrate hematopoietic development and require the coordinate action of growth factor and AML1-like pathways.

Nonequivalent requirements for PS1 and PS2 integrin at cell attachments in Drosophila: genetic analysis of the alpha PS1 integrin subunit

We report on the generation and phenotype of mutant alleles of multiple edematous wings (mew), the gene encoding the alpha PS1 subunit of the PS1 integrin of Drosophila. None of the six alleles examined makes detectable protein, and one allele results from a chromosome break near the middle of the translated sequence, so we are confident that we have described the null phenotype. In contrast to if (alpha PS2) and mys (beta PS) mutants, most mutant mew embryos hatch, to die as larvae. Mutant mew embryos display abnormal gut morphogenesis but, unlike mys or if embryos, there is no evidence of defects in the somatic muscles. Thus, the complementary distributions of PS1 (alpha PS1 beta PS) and PS2 (alpha PS2 beta PS) integrin on tendon cells and muscle, respectively, do not reflect equivalent requirements at the myotendinous junction. Dorsal herniation, characteristic of the mys lethal phenotype, is not observed in mew or in mew if embryos. Clonal analysis experiments indicate that eye morphogenesis is disrupted in mew clones, but if clones in the eye are relatively normal in morphology. Adult wings display blisters around large dorsal but not ventral mew clones. In contrast to dorsal mys clones, small mew patches do not necessarily display morphogenetic abnormalities. Thus, another integrin in addition to PS1 appears to function on the dorsal wing surface.

Notch signaling

The Notch/Lin-12/Glp-1 receptor family mediates the specification of numerous cell fates during development in Drosophila and Caenorhabditis elegans. Studies on the expression, mutant phenotypes, and developmental consequences of unregulated receptor activation have implicated these proteins in a general mechanism of local cell signaling, which includes interactions between equivalent cells and between different cell types. Genetic approaches in flies and worms have identified putative components of the signaling cascade, including a conserved family of extracellular ligands and two cellular factors that may associate with the Notch Intracellular domain. One factor, the Drosophila Suppressor of Hairless protein, is a DNA-binding protein, which suggests that Notch signaling may involve relatively direct signal transmission from the cell surface to the nucleus. Several vertebrate Notch receptors have also been discovered recently and play important roles in normal development and tumorigenesis.

canoe encodes a novel protein containing a GLGF/DHR motif and functions with Notch and scabrous in common developmental pathways in Drosophila

The canoemisty1 (cnomis1) mutation was isolated by virtue of its severe rough eye phenotype from approximately 500 fly lines, each harboring a single autosomal insertion of a P element (Bm delta w). Excision of the P element generated a lethal, null allele, cnomis10, together with many revertants with normal eye morphology. Ommatidia homozygous for cnomis10, produced in an otherwise wild-type eye by somatic recombination, typically contain a reduced number of outer photoreceptors. Some cnomis1 homozygous adults bear extra macrochaetes on the head, notum, humerus and/or scutellum. cnomis1 hemizygotes often show conspicuous wing phenotypes such as a notched blade and the loss of a cross vein. The sequence of cno cDNA clones isolated from an embryonic cDNA library revealed a long open reading frame that potentially encodes a 1893-amino-acid protein with the GLGF/DHR motif, a conserved sequence in Discs large, Dishevelled, and some other proteins associated with cellular junctions. Flies doubly mutant for cnomis1 and scabrous1 (sca1) and those for cnomis1 and the split (spl) allele of Notch (N) always have rumpled wings curved downward. The spl; cnomis1 double mutant flies also exhibit a "giant socket" phenotype. These phenotypes are rarely observed flies singly mutant for either cnomis1, sca1 or spl. The wing vein gaps caused by Abruptex1, a N allele producing an activated form of N protein, are dominantly suppressed by cnomis1. Heterozygosity for shaggy and myospheroid promotes formation of extra wing veins in cnomis1 homozygotes. The genetic interactions suggest that cno participates with members of the N pathway in regulating adhesive cell-cell interactions for the determination of cell fate.

Cytosolic interaction between deltex and Notch ankyrin repeats implicates deltex in the Notch signaling pathway

Genetic data from Drosophila have suggested a functional relationship between the novel cytoplasmic protein encoded by the deltex locus and the transmembrane receptor encoded by Notch. We have demonstrated a direct interaction between these proteins from expression studies conducted in cultured cells, in yeast, and in the imaginal wing disc. deltex binds specifically to the Notch ankyrin repeats, a region that is crucial for Notch signaling and that constitutes the most conserved domain among Notch family members. In addition, we present a new Notch allele, Nsu42c, that is associated with a missense mutation within the fifth ankyrin repeat. In addition to representing a new class of viable Notch allele, this mutation behaves similarly to mutations of deltex and further implicates the ankyrin repeats in Notch function.